Integrated laser with Perot-Fabry cavity

ABSTRACT

A monolithic integrated component ( 10 ) comprises a plurality of sections ( 21, 22 ) including a section ( 21 ) constituting a laser having a cavity delimited by a partially reflecting reflector and at least one other section ( 22 ) adjacent said laser section ( 21 ). The partially reflecting reflector ( 11 ) is disposed between the laser section ( 21 ) and one of the adjacent sections ( 22 ) and is a Bragg reflector grating ( 11 ) that allows multimode operation of the laser ( 21 ).

TECHNICAL FIELD

The field of the invention is that of monolithic integrated componentshaving a plurality of sections including a section constituting aFabry-Perot cavity laser and at least one other section adjacent saidlaser section. It relates to the production of a mirror between thelaser and an adjacent section.

PRIOR ART

In a device including a laser and a modulator, the light emitted by thelaser is coupled into the modulator by means of an optical fiber, forexample. The temperatures of the laser and the modulator are usuallycontrolled to guarantee monomode operation of the laser. For long-haultransmission it is important for the emitted wavelength to remainconstant. To reinforce monomode operation a semi-reflecting faceconstituting an exit face of a Fabry-Perot cavity of the laser istreated so that it is reflective at the operating wavelength of thelaser.

BRIEF DESCRIPTIONS OF THE INVENTION

The present invention relates to a laser and an associated component,for example a modulator, when monomode operation of the laser is notessential, for example a laser used for short-haul transmission overdistances of the order of 2 km or less. This kind of laser does notrequire temperature control. However, because the laser is nottemperature-controlled, operation is no longer monomode and it isimportant for the semi-reflecting exit mirror to allow multimodeoperation. To this end the reflector must have a flat reflectivityresponse, at least for the wavelengths liable to be emitted by the laserat all operating temperatures at which it is likely to operate.

To this end, the invention provides a monolithic integrated componentcomprising a plurality of sections including a section constituting alaser having a cavity delimited by an external face of the component andby a partially reflecting reflector and another section adjacent saidlaser section, which component is characterized in that the partiallyreflecting reflector is disposed between the laser section and saidadjacent other section and in that the reflector allows multimodeoperation of the laser.

In one advantageous embodiment the reflector is a Bragg grating allowingmultimode operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described next with reference to the accompanyingdrawings, in which:

FIG. 1 is a diagram showing a first embodiment of a component of theinvention in section on a plane perpendicular to the plane of the layersand parallel to a direction of propagation of light between two adjacentsections of the component, and

FIG. 2 is a diagram showing a preferred embodiment of a component of theinvention in section on a plane perpendicular to the plane of the layersand parallel to a direction of propagation of light between two adjacentsections of the component.

DESCRIPTION OF EMBODIMENTS

A monolithic component 1 in accordance with the invention as shown inFIG. 1 comprises two sections 21, 22, of which a first section 21 is aFabry-Perot cavity laser and the second section 22 is a subcomponent ofthe component 1. The semiconductor laser first section 21 is made up ofa stack of layers 2, 3, 4, 5, 6 on a substrate and including an activelayer 4 of GaInAsP, for example, and electrical and optical confinementlayers 3, 5. The stack of layers is terminated at the top and at thebottom by respective surface electric contact layers 6 and 2 that areused to bias the laser section 21. The laser layer 4 is bordered aboveand below by the confinement layers 5 and 3, respectively.

A laser cavity 7 is formed in a manner known in the art by cutting thelayers, including the active layer 4, thereby producing mirror faces 8and 9 that are treated to have the necessary coefficients of reflection,so that the active layer 4 is in a Fabry-Perot cavity 7. The lasersection 21 is integrated on the same substrate as the other section 22,which forms a subcomponent, for example a modulator, an amplifier or afilter. One of the mirror faces 9 of the cavity 7 is an external face ofthe component, obtained by cleaving, for example, and the oppositemirror face 8 constitutes an exit face which in practice is obtained byetching at 12 the layers running from one of the surface layers of thecomponent, for example the layer 6, as far as the active layer 4, andpossibly beyond it.

In accordance with the invention, the etched exit face 8 receives areflective treatment so that its reflectivity response is flat at leastfor the operating wavelengths liable to be delivered by the laser overthe range of temperatures in which the laser is likely to operate. Theoperation of the laser is therefore multimode and it is not necessary tocontrol the laser temperature using one of the usual control devices.

It must nevertheless be pointed out that, in an embodiment of this kind,because of the etching at 12, two reflective faces 8 and 18 arenecessarily created, comprising a required first face 8, i.e. the facedelimiting the Fabry-Perot cavity 7, and a second face 18 that isinevitably created, i.e. the face of the second section 22 facing thelaser cavity 7 on the substrate. Because of this, laser light is notreflected towards the cavity 7 by only one mirror (the mirror 8), but bythe two mirrors 8 and 18. It is then necessary to control thereflectivity of the two mirrors 8 and 18 and also that of the opticalpath between them, for example to obtain an even integer number ofhalf-wavelengths. It is difficult to achieve the required accuracy withexisting etching techniques. Also, etching introduces a constantdistance between the reflectors 8 and 18 which is reflected in a phaseshift that varies as a function of the operating wavelength. Because ofthis, the adjustment is correct for only one of the operatingwavelengths of the cavity 7, for example the wavelength corresponding tothe most probable operating temperature, and is degraded at otheroperating temperatures.

The preferred embodiment shown in FIG. 2 has the advantages of the firstembodiment without the drawbacks thereof just described.

FIG. 2 shows a monolithic component 10. The architecture of thecomponent 10 is analogous to that of the component 1 shown in FIG. 1. InFIG. 2, items having the same function as items shown in FIG. 1 areidentified by the same reference number, and these components are notdescribed again. The difference between the component 1 shown in FIG. 1and the component 10 constituting the preferred embodiment of theinvention shown in FIG. 2 lies in the junction between the two sections21 and 22, in that the etching at 12 is no longer present. It isreplaced by a reflective Bragg grating 11 produced by a method known inthe art after depositing the active layer 4. The depth to which thelines constituting the grating are etched is such that the bandwidth ofthe grating allows multimode operation of the laser cavity 7. Thebandwidth can be of the order of ten to a few tens of nanometers, forexample 10 to 20 nanometers. Although the bandwidth of a cleaved facecan be of the order of a few hundred nanometers, a bandwidth of a fewtens of nanometers covering at least the bandwidth of the subcomponentconstituting the second section 22 will not generally lead to anypenalty. The reflectivity of this kind of array in the operating bandcan be of the order of 20 to 25%.

In the example shown in FIG. 2, the second section 22 integrated on thecomponent 10 is a subcomponent known in the art, for example anelectro-absorbant electro-optical modulator.

1. A monolithic integrated component comprising: a laser section havinga cavity delimited by a mirror face and by a Bragg reflector grating,wherein the mirror face is an external face of the monolithic integratedcomponent; and a second section disposed adjacent said laser section,wherein the positioning of the Bragg reflector grating between the lasersection and said second section and the construction of the Braggreflector grating allows multimode operation of the laser.
 2. Themonolithic integrated component according to claim 1, characterized inthat the Bragg reflector grating has a bandwidth from one to a few tensof nanometers.
 3. The monolithic integrated component according to claim2, characterized in that the Bragg reflector grating has a reflectivityof approximately 20 to 25% for wavelengths in its bandwidth.
 4. Themonolithic integrated component according to claim 1, characterized inthat the second section adjacent the laser first section is anelectro-optical modulator.
 5. The monolithic integrated componentaccording to claim 1, characterized in that the Bragg reflector gratingis constructed and arranged to have a flat reflectivity response at theoperating wavelength of the laser section.
 6. A monolithic integratedcomponent, comprising: a laser section having a cavity defined by aBragg reflector grating and a mirror face, the Bragg reflector gratingconstructed and arranged to have a flat reflectivity response at theoperating wavelength of the laser section, and the mirror face anexternal face of the monolithic integrated component; and anelectro-optical modulator disposed adjacent the laser section, whereinthe arrangement of the Bragg reflector grating between the laser sectionand the electra-optical modulator allows multimode operation of thelaser section.
 7. A monolithic integrated component, comprising: a lasersection having a cavity defined by a Bragg reflector grating and amirror face, wherein the mirror face is an external face of themonolithic integrated component; and a second section disposed adjacentthe laser section, wherein the position of the Bragg reflector gratingbetween the laser section and the second section in conjunction with apredetermined bandwidth of the Bragg reflector grating allows multimodeoperation of the laser section.
 8. The monolithic integrated componentaccording to claim 7, characterized in that the second section is anelectro-optical modulator.
 9. The monolithic integrated componentaccording to claim 7, characterized in that the second section is anamplifier.
 10. The monolithic integrated component according to claim 7,characterized in that the second section is a filter.
 11. The monolithicintegrated component according to claim 7, characterized in that theBragg reflector grating has a bandwidth of 10 to 20 nanometers.